OFDMA with block tone assignment for WLAN

ABSTRACT

A plurality of different orthogonal frequency division multiplexing (OFDM) sub-channel blocks are assigned to a plurality of devices including a first device and a second device. The plurality of OFDM sub-channel blocks includes a first OFDM sub-channel block assigned to the first device and a second OFDM sub-channel block assigned to the second device. Data for the first device and data for the second device are received. OFDM data units are generated, wherein data for the first device is modulated on sub-channels in the first OFDM sub-channel block and data for the second device is modulated on sub-channels in the second OFDM sub-channel block. At least one of the OFDM sub-channel blocks is formatted to substantially conform to a physical layer specification of a WLAN communication protocol having a maximum channel bandwidth smaller than a bandwidth of the generated OFDM data units.

CROSS-REFERENCE TO RELATED APPLICATION

This application that claims the benefit of U.S. Provisional PatentApplication No. 61/162,780, entitled “Simple OFDMA with Block ToneAssignment for WLAN,” which was filed on Mar. 24, 2009, the entiredisclosure of which is hereby incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilizeorthogonal frequency division multiplexing (OFDM).

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, and the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps.

These WLANs operate in either a unicast mode or a multicast mode. In theunicast mode, the AP transmits information to one client station at atime. In the multicast mode, the same information is transmitted to agroup of client stations concurrently.

SUMMARY

In one embodiment, a method includes assigning a plurality of differentorthogonal frequency division multiplexing (OFDM) sub-channel blocks toa plurality of devices including a first device and a second device. Theplurality of OFDM sub-channel blocks includes a first OFDM sub-channelblock assigned to the first device and a second OFDM sub-channel blockassigned to the second device. The first device and the second deviceare members of a wireless local area network (WLAN). The method alsoincludes receiving data for the first device, and receiving data for thesecond device. Additionally, the method includes generating OFDM dataunits, wherein data for the first device is modulated on sub-channels inthe first OFDM sub-channel block and data for the second device ismodulated on sub-channels in the second OFDM sub-channel block. The datafor the first device is independent of the data for the second device.At least one of the OFDM sub-channel blocks is formatted tosubstantially conform to a physical layer specification of a WLANcommunication protocol having a maximum channel bandwidth smaller than abandwidth of the generated OFDM data units.

In other embodiments, the method may include one or more of thefollowing features. At least one of the OFDM sub-channel blocks isformatted to substantially conform to at least one of the physical layerspecification of the Institute for Electrical and Electronics Engineers(IEEE) 802.11a Standard and the physical layer specification of the IEEE802.11a Standard.

At least one of the OFDM sub-channel blocks is formatted to conform to adefined communication protocol specification so that the OFDMsub-channel block includes data units that conform to the definedcommunication protocol specification.

Generating the OFDM data units comprises including, in each of aplurality of OFDM sub-channel block data units, a signal that indicatesthe OFDM sub-channel block portion is within an OFDM data unit havingone or more other OFDM sub-channel blocks portions corresponding to oneor more other devices.

Generating the OFDM data units comprises generating a first OFDM dataunit having an OFDM sub-channel block data unit having a duration lessthan a duration of the first OFDM data unit.

Generating the OFDM data units comprises including in the OFDMsub-channel block data unit an indication of the duration of the firstOFDM data unit.

Generating the OFDM data units comprises generating a first OFDM dataunit having a first OFDM sub-channel block data unit corresponding tothe first device and a second OFDM sub-channel block data unitcorresponding to the second device. Additionally, the method furtherincludes zero padding data for the first device so that a duration ofthe first OFDM sub-channel block data unit corresponds to a duration ofthe first OFDM data unit.

Generating the OFDM data units comprises generating a first OFDM dataunit having a first OFDM sub-channel block data unit corresponding tothe first device and a second OFDM sub-channel block data unitcorresponding to the second device. Also, a data rate of the first OFDMsub-channel block data unit is different than a data rate of the secondOFDM sub-channel block data unit.

The method further includes transmitting the OFDM data units.

The method further includes receiving an OFDM data unit including aplurality of acknowledgement or negative acknowledgment signalstransmitted simultaneously by the first device and the second device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a block diagram of an example wireless local area network (WLAN)10, according to an embodiment;

FIGS. 2A, 2B, and 2C are diagrams illustrating example orthogonalfrequency division multiplexing (OFDM) sub-channel blocks for an 80 MHzcommunication channel, according to an embodiment;

FIG. 3 is a diagram of an OFDM symbol that is partitioned into threeOFDM sub-channel blocks for an 80 MHz communication channel;

FIG. 4 is a block diagram of an example downlink orthogonal frequencydivision multiple access (OFDMA) signal, according to an embodiment;

FIG. 5 is a block diagram of an example downlink OFDMA signal, accordingto another embodiment;

FIG. 6 is a diagram illustrating the transmission of a downlink OFDMAdata unit by an access point (AP), and the transmission ofacknowledgment signals (ACKs) by client stations in response to thedownlink OFDMA data unit, according to an embodiment;

FIG. 7 is a diagram illustrating the transmission of a downlink OFDMAdata unit by an AP, and the transmission of ACKs by client stations inresponse to the downlink OFDMA data unit, according to anotherembodiment;

FIG. 8 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment;

FIG. 9 is a flow diagram of another example method that is implementedby an AP in a WLAN, according to an embodiment;

FIG. 10 is a block diagram of an example physical layer (PHY) unit of anAP, according to an embodiment;

FIG. 11 is a block diagram of an example physical layer (PHY) unit of anAP, according to another embodiment;

FIG. 12 is a diagram illustrating communications in a WLAN duringcarrier sense multiple access (CSMA) time periods and an OFDMA timeperiod, according to an embodiment;

FIG. 13 is a diagram illustrating the transmission of an uplink OFDMAdata unit by a plurality of client stations, and the transmission ofACKs by the AP in response to the uplink OFDMA data unit, according toan embodiment;

FIG. 14 is a diagram illustrating the transmission of an uplink OFDMAdata unit being preceded by the AP transmitting downlink synchronizationsignals 520, according to an embodiment;

FIG. 15 is a diagram illustrating communications in a WLAN during CSMAtime periods and an OFDMA time period, according to an embodiment;

FIG. 16 is a flow diagram of an example method that is implemented by anAP in a WLAN, according to an embodiment; and

FIG. 17 is a flow diagram of another example method that is implementedby an AP in a WLAN, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmitsindependent data streams to multiple client stations simultaneously. Inparticular, the wireless device utilizes orthogonal frequency divisionmultiplexing (OFDM) and transmits data for the multiple clients indifferent blocks of OFDM subchannels. Similarly, in embodimentsdescribed below, multiple client stations transmit data to an APsimultaneously, in particular, each client station utilizes OFDM andtransmits data to the AP in a different block of OFDM subchannels.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) unit 18 and a physical layer(PHY) unit 20. The PHY unit 20 includes a plurality of transceivers 21,and the transceivers are coupled to a plurality of antennas 24. Althoughthree transceivers 21 and three antennas 24 are illustrated in FIG. 1,the AP 14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. Two or more of the client stations 25are configured to receive corresponding data streams that aretransmitted simultaneously by the AP 14. Additionally, two or more ofthe client stations 25 are configured to transmit corresponding datastreams to the AP 14 such that the AP 14 receives the data streamssimultaneously.

A client station 25-1 includes a host processor 26 coupled to a networkinterface 27. The network interface 27 includes a MAC unit 28 and a PHYunit 29. The PHY unit 29 includes a plurality of transceivers 30, andthe transceivers are coupled to a plurality of antennas 34. Althoughthree transceivers 30 and three antennas 34 are illustrated in FIG. 1,the client station 25-1 can include different numbers (e.g., 1, 2, 4, 5,etc.) of transceivers 30 and antennas 34 in other embodiments.

In an embodiment, one or more of the client stations 25-2, 25-3, and25-4 has a structure the same as or similar to the client station 25-1.In these embodiments, the client stations 25 structured like the clientstation 25-1 have the same or a different number of transceivers andantennas. For example, the client station 25-2 has only two transceiversand two antennas, according to an embodiment.

According to an embodiment, the client station 25-4 is a legacy clientstation that is not enabled to receive a data stream that is transmittedby the AP 14 simultaneously with other independent data streams that areintended for other client stations 25. Similarly, according to anembodiment, the legacy client station 25-4 is not enabled to transmit adata stream that to the AP 24 at the same time that other clientstations 25 transmit data to the AP 14. According to an embodiment, thelegacy client station 25-4 includes a PHY unit that is generally capableof receiving a data stream that is transmitted by the AP 14simultaneously with other independent data streams that are intended forother client stations 25. But the legacy client station 25-4 includes aMAC unit that is not enabled with MAC layer functions that supportreceiving the data stream that is transmitted by the AP 14simultaneously with other independent data streams that are intended forother client stations 25. According to an embodiment, the legacy clientstation 25-4 includes a PHY unit that is generally capable oftransmitting a data stream to the AP 14 at the same time that otherclient stations 25 transmit data to the AP 14. But the legacy clientstation 25-4 includes a MAC unit that is not enabled with MAC layerfunctions that support transmitting a data stream to the AP 14 at thesame time that other client stations 25 transmit data to the AP 14.

In an embodiment, the legacy client station 25-4 operates according tothe IEEE 802.11a and/or the IEEE 802.11n Standards. The legacy clientstation 25-4, when it communicates with the AP 14, occupies an entirecommunication channel. For example, the IEEE 802.11a Standard definescommunication channels each having a width of 20 MHz. When the AP 14 andthe legacy client station 25-4 communicate according to the IEEE 802.11aStandard, the AP 14 transmits data to the legacy client station 25-4 in64 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 64 OFDMsubchannels. The IEEE 802.11n Standard defines 20 MHz and 40 MHzcommunications channels. When the AP 14 and the legacy client station25-4 communicate according to the IEEE 802.11n Standard using a 20 MHzchannel, the AP 14 transmits data to the legacy client station 25-4 in64 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 64 OFDMsubchannels. When the AP 14 and the legacy client station 25-4communicate according to the IEEE 802.11n Standard using a 40 MHzchannel, the AP 14 transmits data to the legacy client station 25-4 in128 OFDM subchannels that occupy the entire channel, and the legacyclient station 25-4 transmits data to the AP 14 in the 128 OFDMsubchannels.

According to the IEEE 802.11a and the IEEE 802.11n Standards, differentdevices share the communication channel by utilizing a carrier sense,multiple access (CSMA) protocol. Generally speaking, CSMA, according tothe IEEE 802.11a and the IEEE 802.11n Standards, specifies that a devicethat wishes to transmit should first check whether another device in theWLAN is already transmitting. If another device is transmitting, thedevice should wait for a time period and then again check again to seewhether the communication channel is being used. If a device detectsthat the communication channel is not being used, the device thentransmits using the channel. With CSMA, in other words, data that is fora particular device (i.e., not multicast data) can only be transmittedon the channel when no other data is being transmitted on the channel.

According to an embodiment, the AP 14 is enabled to transmit differentdata streams to different client stations 25 at the same time. Inparticular, the PHY unit 20 is configured to transmit in a communicationchannel that is wider than specified by the IEEE 802.11a and the IEEE802.11n Standards. For example, the PHY unit 20 is configured totransmit in one or more of an 80 MHz communication channel, a 120 MHzcommunication channel, and/or a 160 MHz communication channel, accordingto an embodiment. As another example, the PHY unit 20 is additionallyconfigured to transmit in one or more of a 200 MHz communicationchannel, a 240 MHz communication channel, a 280 MHz communicationchannel, etc., according to an embodiment.

According to an embodiment, the AP 14 is configured to partition thewider communication channel into narrower sub-bands or OFDM sub-channelblocks, and different data streams for different client devices 25 aretransmitted in respective OFDM sub-channel blocks. According to anembodiment, each OFDM sub-channel block substantially conforms to thePHY specification of the IEEE 802.11a Standard. According to anotherembodiment, each OFDM sub-channel block substantially conforms to thePHY specification of the IEEE 802.11n Standard. According to anotherembodiment, each OFDM sub-channel block substantially conforms to a PHYspecification of a communication protocol other than the IEEE 802.11aand the IEEE 802.11n Standards.

As used herein, the phrase “OFDM sub-channel block substantiallyconforms to the PHY specification” of a communication protocol orstandard generally means that a device (configured according to thecommunication protocol or standard) that receives the transmitted OFDMsub-channel block is able, generally, to detect and decode the data inthe OFDM sub-channel block (signal strength, signal-to-noise (SNR),interference, etc., permitting). For example, an OFDM sub-channel blockthat substantially conforms to the PHY specification of a communicationprotocol or standard utilizes the modulation, tone mapping, pilotlocations, etc., set forth in the communication protocol or standard,although other aspects of the OFDM sub-channel block do not conform tothe PHY specification, according to an embodiment. For example, theremay be more zero tones at the edges of an OFDM sub-channel block,reduced power (by frequency domain power allocation) at edge tones,etc., than called for by the communication protocol or standard.Similarly, a used herein, the phrase “a device configured tosubstantially conform to the PHY specification” of a communicationprotocol or standard generally means that the device is able to detectand decode a signal that conforms or an OFDM sub-channel block thatsubstantially conforms to the communication protocol or standard (signalstrength, signal-to-noise (SNR), interference, etc., permitting). Thephrase “a device configured to substantially conform to the PHYspecification” of a communication protocol or standard also generallymeans that the device is able to generate a signal that conforms or anOFDM sub-channel block that substantially conforms to the communicationprotocol or standard.

When an OFDM sub-channel block substantially conforms to the PHYspecification of the IEEE 802.11a Standard, for example, a client device25 corresponding to the OFDM sub-channel block utilizes a PHY unit 29configured (or substantially configured) according to the IEEE 802.11aStandard to receive the data stream transmitted in the OFDM sub-channelblock. When an OFDM sub-channel block substantially conforms to the PHYspecification of the IEEE 802.11n Standard, for example, a client device25 corresponding to the OFDM sub-channel block utilizes a PHY unit 29configured (or substantially configured) according to the IEEE 802.11nStandard to receive the data stream transmitted in the OFDM sub-channelblock.

According to an embodiment, each OFDM sub-channel block includes acontiguous block of OFDM sub-channels or tones that can be demodulatedat the client station using a fast Fourier transform (FFT) with a widththe size of the OFDM sub-channel block. In other words, according tothis embodiment, the OFDM sub-channels assigned to client stations arenot interleaved such as in the Wi-Max standard.

FIGS. 2A, 2B, and 2C are diagrams illustrating example OFDM sub-channelblocks for an 80 MHz communication channel, according to an embodiment.In FIG. 2A, the communication channel is partitioned into fourcontiguous OFDM sub-channel blocks, each having a bandwidth of 20 MHz.The OFDM sub-channel blocks include independent data streams for fourclient stations. In FIG. 2B, the communication channel is partitionedinto two contiguous OFDM sub-channel blocks, each having a bandwidth of40 MHz. The OFDM sub-channel blocks include independent data streams fortwo client stations. In FIG. 2C, the communication channel ispartitioned into three contiguous OFDM sub-channel blocks. Two OFDMsub-channel blocks each have a bandwidth of 20 MHz. The remaining OFDMsub-channel block has a bandwidth of 40 MHz. The OFDM sub-channel blocksinclude independent data streams for three client stations.

Although in FIGS. 2A, 2B, and 2C, the OFDM sub-channel blocks arecontiguous across the communication channel, in other embodiments theOFDM sub-channel blocks are not contiguous across the communicationchannel (i.e., there are one or more gaps between the OFDM sub-channelblocks). In an embodiment, each gap is at least as wide as one of theOFDM sub-channel blocks. In another embodiment, at least one gap is lessthan the bandwidth of an OFDM sub-channel block. In another embodiment,at least one gap is at least as wide as 1 MHz. In an embodiment,different OFDM sub-channel blocks are transmitted in different channelsdefined by the IEEE 802.11a and/or 802.11n Standards. In one embodiment,the AP includes a plurality of radios and different OFDM sub-channelblocks are transmitted using different radios.

In an embodiment, for a plurality of data streams transmitted by an APin different OFDM sub-channel blocks, different data streams aretransmitted at different data rates when, for example, signal strength,SNR, interference power, etc., varies between client devices.Additionally, for a plurality of data streams transmitted by an AP indifferent OFDM sub-channel blocks, the amount of data in different datastreams is often different. Thus, one transmitted data stream can endbefore another. In such situations, the data in an OFDM sub-channelblock corresponding to data stream that is ended is set to zero or someother suitable predetermined value, according to an embodiment. FIG. 3is a diagram of an (n+1)-th OFDM symbol that is partitioned into threecontiguous OFDM sub-channel blocks for an 80 MHz communication channel.Two OFDM sub-channel blocks, corresponding to a Station 1 and a Station3 each have a bandwidth of 20 MHz. The remaining OFDM sub-channel block,corresponding to a Station 2, has a bandwidth of 40 MHz. The OFDMsub-channel blocks include independent data streams for the threestations. The data stream corresponding to Station 2 ended in the n-thOFDM symbol (i.e., the OFDM symbol previous to the (n+1)-th OFDMsymbol), whereas the data streams corresponding to Station 1 and Station2 have not yet ended. Thus, for the (n+1)-th OFDM symbol, data in theOFDM sub-channel block corresponding to a Station 2 is set to zero.

An OFDM signal comprising a plurality of OFDM sub-channel blocks totransmit independent data streams as described above is also referred toherein as an orthogonal frequency division multiple access (OFDMA)signals. According to an embodiment, a WLAN utilizes downlink OFDMAsignals and uplink OFDMA signals. Downlink OFDMA signals are transmittedsynchronously from a single AP to multiple client stations (i.e.,point-to-multipoint). An uplink OFDMA signal is transmitted by multipleclients stations jointly to a single AP (i.e., multipoint-to-point).Frame formats and/or signaling schemes for downlink OFDMA and uplinkOFDMA are different, according to some embodiments.

Embodiments of a PHY frame format for downlink OFDMA signals will now bedescribed. In the following embodiments, OFDM sub-channel blocks have aformat substantially similar to the PHY format specified in the IEEE802.11n Standard. In other embodiments, OFDM sub-channel blocks have aformat substantially similar to another communication protocol such asthe PHY format specified in the IEEE 802.11a Standard or a communicationprotocol not yet standardized.

FIG. 4 is a block diagram of an example downlink OFDMA signal 100,according to an embodiment, that is partitioned into four equal-widthOFDM sub-channel blocks 102 corresponding to four client stations. Inthe embodiment of FIG. 4, each OFDM sub-channel block 102 has a formatsubstantially similar to the “mixed mode” data unit PHY format specifiedin the IEEE 802.11n Standard. For example, each OFDM sub-channel blockincludes a preamble 104 including a legacy short training field (L-STF),a legacy long training field (L-LTF), a legacy signal (L-SIG) field, ahigh throughput signal (HT-SIG) field, a high throughput short trainingfield (HT-STF), and one or more high throughput long training fields(HT-LTF). Additionally, each OFDM sub-channel block includes a highthroughput data field 108 (HT-DATA). The duration of the high throughputportion of the downlink OFDMA signal 100 is T, which corresponds to thelongest of the four OFDM sub-channel blocks 102 (i.e., 102-4). In otherwords, the durations of the high throughput portions of the OFDMsub-channel blocks 102-1, 102-2, and 102-3 are shorter than the durationof the high throughput portion of the downlink OFDMA signal 100.

The legacy portion of the preamble 104 (i.e., L-STF, L-LTF, and L-SIG)is identical in all of the OFDM sub-channel blocks 102, according to anembodiment. For the high throughput portion of the preamble 104 (i.e.,starting with HT-SIG), the content of the OFDM sub-channel blocks 102can be variant for different client stations depending on factors suchas rate, data quantity, configuration (e.g., number of antennas, numberof supported multiple input, multiple output (MIMO) data streams, etc.)of different clients.

According to an embodiment, the AP sets the “reserved bit” in each ofthe L-SIG fields to “1” (the IEEE 802.11a and 802.11n Standards specifythat the “reserved bit” in L-SIG to “0”) to signal the receiver that thecurrent data unit is a downlink OFDMA signal. Additionally, the AP setsthe Length and Rate sub-fields in each off the L-SIG fields tocorrespond to T, the duration of the high throughput portion of thelongest OFDM sub-channel block 102 (i.e., 102-4). According to anotherembodiment, the AP sets the “reserved bit” in each of the HT-SIG fieldsto “0” (the IEEE 802.11n Standard specifies that the “reserved bit” inHT-SIG to “1”) to signal the receiver that the current data unit is adownlink OFDMA signal.

In other embodiments, the AP signals that a data unit is a downlinkOFDMA signal using techniques other than those described above. Forexample, according to one embodiment, the AP uses MAC layer signaling toreserve a time period for transmitting a downlink OFDMA signal. In thisembodiment, MAC layer signaling is utilized to specify the duration T ofthe downlink OFDMA signal 100. In another embodiment, MAC layersignaling does not specify the duration T of the downlink OFDMA signal100, but rather specifies different respective times at which respectiveclient stations should send respective acknowledgments of the downlinkOFDMA signal 100. In another embodiment, the AP utilizes MAC layersignaling to specify a single time at which all client stationscorresponding to the downlink OFDMA signal 100 should simultaneouslytransmit respective acknowledgments.

In one embodiment, each OFDM sub-channel block 102 in FIG. 4 has a widthof 20 MHz. In another embodiment, each OFDM sub-channel block 102 inFIG. 4 has a width of 40 MHz. According to an embodiment, if an OFDMsub-channel block has a width of 40 MHz, the legacy portion of thepreamble 104 (i.e., L-STF, L-LTF, and L-SIG) is duplicated at upper andlower 20 MHz halves, with the sub-channels in the upper 20 MHz phaseshifted by 90 degrees with respect to the sub-channels in the lower 20MHz.

FIG. 5 is a block diagram of an example downlink OFDMA signal 150,according to an embodiment, that is partitioned into four equal-widthOFDM sub-channel blocks 152 corresponding to four client stations. Inthe embodiment of FIG. 5, each OFDM sub-channel block 152 has a formatsubstantially similar to the “Green field mode” data unit PHY formatspecified in the IEEE 802.11n Standard. For example, each OFDMsub-channel block includes a preamble 154 including an HT-SIG field, andHT-STF field, and one or more HT-LTF fields. Additionally, each OFDMsub-channel block 152 includes a high throughput data field 158(HT-DATA). The duration of the downlink OFDMA signal 100 is T. Theduration of each OFDM sub-channel block 152 is also T. In other words,the AP controls the duration of each OFDM sub-channel block 152 to be T,according to an embodiment. In one embodiment, the AP utilizes zeropadding to ensure that each OFDM sub-channel block 152 has a duration ofT. In one embodiment, a MAC unit of the AP zero pads one or more MACservice data units (MSDUs) that are included in a MAC protocol data unit(MPDU), which is in turn included in a PHY protocol data unit (PPDU). Byzero padding an MSDU, for example, the lengths of the MPDU and the PPDUare increased.

In an embodiment, the AP uses MAC layer signaling to reserve a timeperiod for transmitting the downlink OFDMA signal 150. In oneembodiment, MAC layer signaling is utilized to specify the duration T ofthe downlink OFDMA signal 150. In another embodiment, MAC layersignaling does not specify the duration T of the downlink OFDMA signal150, but rather specifies different respective times at which respectiveclient stations should send respective acknowledgments of the downlinkOFDMA signal 150. In another embodiment, the AP utilizes MAC layersignaling to specify a single time at which all client stationscorresponding to the downlink OFDMA signal 150 should simultaneouslytransmit respective acknowledgments.

In another embodiment, a downlink OFDMA signal includes one or more OFDMsub-channel blocks that have a format substantially similar to the“mixed mode” data unit PHY format specified in the IEEE 802.11n Standardand one or more OFDM sub-channel blocks that have a format substantiallysimilar to the “Green field mode” data unit PHY format specified in theIEEE 802.11n Standard. In one implementation, the AP forms the downlinkOFDMA signal so that the duration of each of the OFDM sub-channel blocksis the same. In another implementation, the duration of each of the OFDMsub-channel blocks need not be the same.

In another embodiment, a downlink OFDMA signal includes one or more OFDMsub-channel blocks that conform to a defined communication protocolspecification, such as the IEEE 802.11ac Standard now in the process ofbeing adopted, so that each OFDM sub-channel block in the OFDMA dataunit forms an OFDM data unit. In some embodiments, information inpreambles of OFDM sub-channel blocks of an OFDMA data unit indicate orsignals that each OFDM sub-channel block is part of an OFDMA data unit.In an embodiment, such signaling information is included in a suitablepreamble field such as a field that is the same as or similar to theL-SIG field and/or the HT-SIG field specified in the IEEE 802.11a andIEEE 802.11n Standards.

In some embodiments, client stations respond with an acknowledgmentsignal (ACK) or a negative ACK signal (NAK) after the AP transmits eachdownlink OFDMA data unit or after the AP transmits a plurality ofdownlink OFDMA data units (referred to as “Block ACK”). FIG. 6 is adiagram illustrating the transmission of a downlink OFDMA data unit 200by an AP, and the transmission of ACKs 204 by client stations inresponse to the downlink OFDMA data unit 200, according to anembodiment. In the scenario illustrated in FIG. 6, four client stationssuccessfully received data transmitted in the downlink OFDMA data unit200. In response, each of the four client stations transmits an ACK 204simultaneous with the transmission of the other ACKs 204. The ACKs aretransmitted after a short inter-frame space (SIFS) interval. In the IEEE802.11n Standard, SIFS is specified as 16 microseconds, but any suitableSIFS period can be utilized, depending on the particular implementation.In an embodiment, the downlink OFDMA data unit 200 and the ACKs 204 aretransmitted in a time period reserved for OFDMA transmissions in theWLAN. According to an embodiment, client stations transmit ACKs/NAKs byan uplink OFDMA data unit, which will be discussed in more detail below.Each client station transmits the ACK 204 in a different OFDMsub-channel block.

In one embodiment, each client station determines when to transmit anACK/NAK based on a determined duration of the OFDMA data unit 200. Asdiscussed above with respect to FIG. 4, the AP can provide informationin the OFDMA data unit 200 that indicates the duration of the OFDMA dataunit 200, and a client station can use this information to determinewhen to transmit the ACK 204. In another embodiment, the AP assigns atime slot to the client stations in which each client station cantransmit an ACK/NAK. For example, a MAC unit in the AP can signal, in anOFDMA data unit previous to the OFDMA data unit 200, the time period inwhich the client stations are to transmit ACKs/NAKs.

FIG. 7 is a diagram illustrating the transmission of a downlink OFDMAdata unit 250 by an AP, and the transmission of ACKs 254 by clientstations in response to the downlink OFDMA data unit 250, according toan embodiment. In the scenario illustrated in FIG. 7, four clientstations successfully received data transmitted in the downlink OFDMAdata unit 250. In response, each of the four client stations transmitsan ACK 254 at different specified times. The downlink OFDMA data unit250 and the ACKs are transmitted in a time period reserved for OFDMA. AMAC unit of the AP has signaled each of the client stations providingeach client station with an indication of the time at which the clientstation can transmit an ACK/NAK. For example, according to anembodiment, the MAC unit of the AP provides ACK/NAK time slotinformation to the client stations when providing information regardingthe reserved time period for OFDMA.

The ACKs are spaced by SIFS intervals. In an embodiment, the downlinkOFDMA data unit 250 and the ACKs 254 are transmitted in a time periodreserved for OFDMA transmissions in the WLAN. According to anembodiment, client stations transmit ACKs/NAKs by an uplink OFDMA dataunit, which is discussed in more detail below. Each client stationtransmits the ACK 254 in a different OFDM sub-channel block.

In an embodiment, the AP assigns the time slots to the client stationsin which each client station can transmit the ACKs/NAKs. For example, aMAC unit in the AP can signal, in an OFDMA data unit previous to theOFDMA data unit 250, the time period in which a client stations is totransmit an ACK/NAK.

In another embodiment, ACKs/NAKs are transmitted by the client stationsafter receiving a plurality of downlink OFDMA data units (referred to as“Block ACK”). In this embodiment, a client station determines when totransmit a Block ACK based on determining a duration of a downlink OFDMAdata unit or transmits in a time slot assigned by the AP, for example.

In an embodiment, the downlink OFDMA signal is configured to be receivedand decoded by a legacy client station (e.g., a client stationconfigured to communicate according to the IEEE 802.11a Standard and/orthe IEEE 802.11n Standard). In an embodiment, the AP does not signal toat least the legacy client stations that an OFDMA data unit is an OFDMAsignal (as opposed to an OFDM data unit according to the legacy protocol(e.g., the IEEE 802.11a Standard and/or the IEEE 802.11n Standard). Inan embodiment, at least OFDM sub-channel blocks corresponding to legacyclient stations have the same duration as the downlink OFDMA signal sothat ACKs/NAKs transmitted by the legacy client station occur atappropriate times with respect to the OFDMA data unit.

FIG. 8 is a flow diagram of an example method 300 that is implemented byan AP in a WLAN, according to an embodiment. At block 304, a pluralityof different OFDM sub-channel blocks are assigned to a plurality ofdifferent client stations. At block 308, a plurality of independent datastreams (i.e., the streams include different data) are received, whereineach data stream corresponds to a respective client station, and thedata streams are to be transmitted to the client stations. At block 312,downlink OFDM data units are generated such that the plurality ofindependent data streams are modulated in respective OFDM sub-channelblocks. In an embodiment, generating downlink OFDM data units comprisesincluding an indication in a downlink OFDM data unit that the data unitis an OFDMA data unit (i.e., the data unit includes multiple OFDMsub-channel blocks corresponding to different client stations. In anembodiment, generating downlink OFDM data units comprises including anindication in an OFDM sub-channel block of a duration of a downlink OFDMdata unit (i.e., an indication of a duration of the longest durationOFDM sub-channel block in the OFDMA data unit) separate from anindication of the duration of the OFDM sub-channel block. According toan embodiment, the indication of the duration of the downlink OFDM dataunit includes an indication of a rate and an indication of a lengthcorresponding to the longest duration OFDM sub-channel block in theOFDMA data unit.

At block 316, the AP transmits the OFDM data units generated at block312.

FIG. 9 is a flow diagram of an example method 350 that is implemented byan AP in a WLAN, according to an embodiment. In an embodiment, themethod 350 is implemented in conjunction with the method 300 of FIG. 8.

At block 354, the AP determines a time period that is reserved fordownlink OFDMA signals. In one embodiment, the AP also determines a timeor times at which client stations can transmit ACKs/NAKs or Block ACKsin response to downlink OFDMA data units.

At block 358, the AP transmits to the client stations data indicative ofthe time period determined at block 354. In one embodiment, the AP alsotransmits data indicative of the time or times at which client stationscan transmit ACKs/NAKs or Block ACKs in response to downlink OFDMA dataunits.

FIG. 10 is a block diagram of an example PHY unit 400 of an AP,according to an embodiment. Referring again to FIG. 1, the PHY unit 20of the AP 14 includes the PHY unit 400 of FIG. 10, in an embodiment.

The PHY unit 400 includes a plurality of processing blocks 404. In anembodiment, each processing block 404 performs forward error correction(FEC) encoding, modulation, and spatial mapping functions in a mannerthe same as or similar to such functions described in the IEEE 802.11aStandard and/or the IEEE 802.11n Standard. In FIG. 10, four processingblocks 404 are illustrated. In other embodiments, a different number ofprocessing blocks 404 are included. For example, in one embodiment, asingle processing block 404 is time-shared to process multiple datastreams received in parallel.

The processing blocks 404 receive a plurality of independent datastreams to be transmitted to a plurality of client devices. In theembodiment of FIG. 10, each processing block 404 processes a differentone of the independent data streams and generates a plurality ofconstellation points corresponding to a plurality of OFDM sub-channels.

Outputs of the processing blocks 404 are provided to a mapping unit 408.The mapping unit 408 concatenates constellation points from theprocessing blocks 404 into a larger width OFDM symbol. For example, ifthe output of each processing block 404 corresponds to a 20 MHz wide(64-point inverse fast Fourier transform (IFFT)) OFDM symbol, then themapping unit 408 concatenates the outputs of the processing blocks 404into an 80 MHz wide (256-point IFFT). As another example, if the outputof each processing block 404 corresponds to a 40 MHz wide (128-pointIFFT) OFDM symbol, then the mapping unit 408 concatenates the outputs ofthe processing blocks 404 into a 160 MHz wide (512-point IFFT).

An IFFT unit 412 generates a time-domain signal from the output of themapping unit 408. In an embodiment, the IFFT unit 412 has a width largerthan in a typical AP configured to implement the IEEE 802.11a Standardand/or the IEEE 802.11n Standard. In one embodiment, the IFFT unit 412implements a 256-point IFFT. In another embodiment, the IFFT unit 412implements a 512-point IFFT. In another embodiment, the IFFT unit 412implements a suitable width IFFT other than a 256-point IFFT or a512-point IFFT.

A digital processing and digital-to-analog converter (DAC) block 416processes the output of the IFFT unit 412 and generates an analogsignal. In an embodiment, the digital processing and DAC block 416includes a guard interval insertion unit. In another embodiment, thedigital processing and DAC block 416 includes a windowing unit to smoothedges of each OFDM symbol. In an embodiment, the digital processing andDAC block 416 is configured to process signals with a larger bandwidthas compared to a similar processing block in a typical AP configured toimplement the IEEE 802.11a Standard and/or the IEEE 802.11n Standard. Inone embodiment, the digital processing and DAC block 416 is configuredto process signals with a bandwidth of 80 MHz. In another embodiment,the digital processing and DAC block 416 is configured to processsignals with a bandwidth of 160 MHz. In another embodiment, the digitalprocessing and DAC block 416 is configured to process signals with abandwidth different than 80 MHz or 160 MHz.

A radio frequency (RF) modulation block 420 generally upconverts theoutput of the digital processing and DAC block 416 to generate an RFsignal, which is transmitted by an antenna 424. In an embodiment, the RFmodulation block 420 is configured to process signals with a largerbandwidth as compared to a similar RF block in a typical AP configuredto implement the IEEE 802.11a Standard and/or the IEEE 802.11n Standard.In one embodiment, the RF modulation block 420 is configured to processsignals with a bandwidth of 80 MHz. In another embodiment, the RFmodulation block 420 is configured to process signals with a bandwidthof 160 MHz. In another embodiment, the RF modulation block 420 isconfigured to process signals with a bandwidth different than 80 MHz or160 MHz.

In an embodiment, the PHY unit 400 is a sub-unit in a MIMO PHY unit. Inthis embodiment, the MIMO PHY unit includes a plurality of digitalprocessing and DAC blocks 416 and a plurality of RF modulation blocks420 corresponding to a plurality of antennas 424. In another embodiment,the MIMO PHY unit includes a plurality of mapping units 408 and aplurality of IFFT units 412 corresponding to a plurality of transmitchains. In this embodiment, each processing block 404 generates aplurality of outputs corresponding to a plurality of spatially mappedtransmit chain signals. In another embodiment, the MIMO PHY unitincludes a beamforming unit.

FIG. 11 is a block diagram of an example PHY unit 450 of an AP,according to another embodiment. Referring again to FIG. 1, the PHY unit20 of the AP 14 includes the PHY unit 450 of FIG. 11, in an embodiment.

The PHY unit 450 includes the plurality of processing blocks 404 of FIG.10. A plurality of IFFT units 454 generate time-domain signals from theoutputs of the processing blocks 404. In an embodiment, each IFFT unit454 has a width such as in a typical AP configured to implement the IEEE802.11a Standard and/or the IEEE 802.11n Standard. In one embodiment,each IFFT unit 454 implements a 64-point IFFT. In another embodiment,each IFFT unit 454 implements a 128-point IFFT. In another embodiment,each IFFT unit 454 implements a suitable width IFFT other than a64-point IFFT or a 128-point IFFT.

A plurality of digital processing and DAC blocks 458 process the outputsof the IFFT units 454 and generate corresponding analog signals. In anembodiment, each digital processing and DAC block 458 includes a guardinterval insertion unit. In another embodiment, each digital processingand DAC block 458 includes a windowing unit to smooth edges of each OFDMsymbol. In an embodiment, each digital processing and DAC block 458 isconfigured to process signals having a bandwidth such as in a typical APconfigured to implement the IEEE 802.11a Standard and/or the IEEE802.11n Standard. In one embodiment, each digital processing and DACblock 458 is configured to process signals with a bandwidth of 20 MHz.In another embodiment, each digital processing and DAC block 458 isconfigured to process signals with a bandwidth of 40 MHz. In anotherembodiment, each digital processing and DAC block 458 is configured toprocess signals with a bandwidth different than 20 MHz or 40 MHz.

A plurality of RF modulation blocks 462 generally upconvert the outputsof the digital processing and DAC block 458 to generate RF signals,which are transmitted by respective antennas 466. In an embodiment, eachRF modulation block 462 is configured to process signals having abandwidth such as in a typical AP configured to implement the IEEE802.11a Standard and/or the IEEE 802.11n Standard. In one embodiment,each RF modulation block 462 is configured to process signals with abandwidth of 20 MHz. In another embodiment, each RF modulation block 462is configured to process signals with a bandwidth of 40 MHz. In anotherembodiment, each RF modulation block 462 is configured to processsignals with a bandwidth different than 20 MHz or 40 MHz.

In an embodiment, the PHY unit 450 is a sub-unit in a MIMO PHY unit. Inone embodiment, the MIMO PHY unit includes an additional set of one ormore of the IFFT units 454, the digital processing and DAC blocks 458,and the RF modulation blocks 462 for each of a plurality of transmitchains. In one embodiment, the MIMO PHY unit includes a beamformingunit.

In one embodiment, the AP utilizes a single MAC address for thedifferent OFDM sub-channel blocks. In an embodiment, the AP includes aMAC unit that includes a plurality of transmit/receive processing blockscorresponding to the plurality of client devices with which the AP iscommunicating using OFDMA signals such as described above. The pluralityof transmit/receive processing blocks in the MAC unit process theindependent data streams simultaneously and/or in parallel.

In an embodiment, a client station that supports OFDMA signaling asdescribed above includes a modified PHY unit (as compared to a PHY unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified PHY unit is configuredto determine when a received data unit is within an OFDMA data unit,according to an embodiment. For instance, the PHY unit examines theL-SIG and/or HT-SIG “reserved” bits to detect an OFDMA data unit, in anembodiment. As another example, the modified PHY unit is configured todetermine when an OFDMA data unit will end, as opposed to an OFDMsub-channel block within the OFDMA data unit that corresponds to theclient station, according to an embodiment. For instance, the PHY unitexamines the Length and Rate subfields in the L-SIG field to determine aduration of the OFDMA data unit for purposes of determining when totransmit an ACK/NAK, in an embodiment.

In an embodiment, a client station that supports OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto interpret MAC signals from the AP regarding when the client cantransmit ACKs/NAKs or Block ACKs, according to an embodiment. As anotherexample, the modified MAC unit is configured to interpret MAC signalsfrom the AP regarding periods reserved for OFDMA signals.

In an embodiment, a combination of PHY and MAC signaling is utilized forindicating OFDMA data units, the duration of OFMDA data units, and/orreserved time slots for OFDMA signals. In this embodiment, a clientstation that supports OFDMA signaling as described above includes amodified PHY unit and a modified MAC unit, such as described above.

FIG. 12 is a diagram illustrating communications in a WLAN 470 duringthree time periods: a first CSMA period 474, an OFDMA time period 478,and a second CSMA period 482. In FIG. 12, time progresses from left toright so that the first CSMA period 474 occurs first, the OFDMA timeperiod 478 occurs second, and the second CSMA period 482 occurs third.The WLAN includes an AP, a plurality of legacy client stations (LCs),and a plurality of OFDMA client stations (OC).

In the first CSMA period 474, the AP transmits a legacy downlink singleto one of the LCs. The OFDMA period 478 is reserved for OFDMA signaltransmissions. Thus, in the OFDMA period 478, the AP transmits adownlink OFDMA signal to a plurality of OCs. The downlink OFDMA signalincludes a plurality of OFDM sub-channel blocks corresponding to theplurality of OCs. In the OFDMA period 478, the plurality of OCs alsotransmit ACKs/NAKs (not shown) in response to the downlink OFDMA signal,according to an embodiment. In the second CSMA period 482, an LCtransmits a legacy uplink transmission to the AP.

Embodiments of a PHY frame format for uplink OFDMA signals will now bedescribed. In the following embodiments, OFDM sub-channel blocks have aformat substantially similar to the PHY format specified in the IEEE802.11n Standard. In other embodiments, OFDM sub-channel blocks have aformat substantially similar to another communication protocol such asthe PHY format specified in the IEEE 802.11a Standard or a communicationprotocol not yet standardized.

An uplink OFDMA signal comprises a plurality of OFDM sub-channel blocks,a plurality of which are transmitted by different client stations. Inone embodiment, each OFDM sub-channel block substantially conforms tothe “mixed mode” format as specified in the IEEE 802.11n Standard. Inanother embodiment each OFDM sub-channel block substantially conforms tothe “Green field” format as specified in the IEEE 802.11n Standard. Inanother embodiment, the OFDM sub-channel blocks in an uplink OFDMA dataunit are mixture of “mixed mode” and “Green field” substantiallyformatted data units.

In one embodiment, an uplink OFDMA data unit with mixed mode OFDMsub-channel blocks transmitted by the plurality of clients has a formatthe same as or similar to the format illustrated in FIG. 4. According toone embodiment, the L-SIG “reserved” bit is not set to indicate an OFDMAdata unit. According to another embodiment, each client station sets theL-SIG “reserved” bit if the client station is aware that the OFDMsub-channel block that the client station is transmitting is part of anuplink OFDMA data unit. According to another embodiment, each clientstation does not set the Length and Rate subfields in the L-SIG fielddifferently than when transmitting a CSMA signal. According to anotherembodiment, each client station sets Length and Rate subfields in theL-SIG field to correspond to the duration of the uplink OFDMA data unitif the client station is aware of the duration of the uplink OFDMA dataunit.

In one embodiment, the AP reserves a time period for transmission ofuplink OFDMA signals. In this embodiment, the AP transmits informationregarding the starting time, ending time, and/or duration of thereserved time period to the client stations.

According to an embodiment, an AP capable of receiving an uplink OFDMAsignal includes an RF demodulation block, an analog-to-digital converter(ADC) and processing block, and an FFT unit that are configured toprocess signals with a larger bandwidth as compared to similar blocks ina typical AP configured to implement the IEEE 802.11a Standard and/orthe IEEE 802.11n Standard. In one embodiment, these blocks areconfigured to process signals with a bandwidth of 80 MHz. In anotherembodiment, these blocks are configured to process signals with abandwidth of 160 MHz. In another embodiment, these blocks are configuredto process signals with a bandwidth different than 80 MHz or 160 MHz.

In another embodiment, an AP capable of receiving an uplink OFDMA signalincludes a plurality of RF demodulation blocks, a plurality of ADC andprocessing blocks, and a plurality of FFT units that are configured toprocess signals process signals having a bandwidth such as in a typicalAP configured to implement the IEEE 802.11a Standard and/or the IEEE802.11n Standard. In one embodiment, each such block is configured toprocess signals with a bandwidth of 20 MHz. In another embodiment, eachsuch block is configured to process signals with a bandwidth of 40 MHz.In another embodiment, each such block is configured to process signalswith a bandwidth different than 20 MHz or 40 MHz. In these embodiments,the plurality of blocks operate in parallel to process each OFDMsub-channel block, which has a smaller bandwidth than the uplink OFDMAsignal, in parallel.

In one embodiment, the AP utilizes a single MAC address for receivingdifferent OFDM sub-channel blocks. In an embodiment, the AP includes aMAC unit that includes a plurality of receive processing blockscorresponding to the plurality of client devices with which the AP iscommunicating using OFDMA signals such as described above. The pluralityof receive processing blocks in the MAC unit process the independentdata streams received from the client stations simultaneously and/or inparallel.

In an embodiment, an AP that supports uplink OFDMA signaling asdescribed above includes a modified PHY unit (as compared to a PHY unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified PHY unit is configuredto operate at a wider bandwidth as described above, according to anembodiment.

In an embodiment, an AP that supports uplink OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto determine when the AP can transmit ACKs/NAKs or Block ACKs, accordingto an embodiment. As another example, the modified MAC unit isconfigured to reserve time periods for uplink OFDMA signals.

In an embodiment, a legacy AP is capable of receiving and decoding datatransmitted in an OFDM sub-channel block by a client station as part ofan uplink OFDMA signal.

In an embodiment, a client that supports uplink OFDMA signaling asdescribed above merely implements a PHY data unit that conforms to theIEEE 802.11a Standard and/or the IEEE 802.11n Standard. In anotherembodiment, a client that supports uplink OFDMA signaling as describedabove includes a modified PHY unit (as compared to a PHY unit configuredto operate according to the IEEE 802.11a Standard and/or the IEEE802.11n Standard). For example, the modified PHY unit is configured toperform PHY signaling regarding uplink OFDMA.

In an embodiment, a client that supports uplink OFDMA signaling asdescribed above includes a modified MAC unit (as compared to a MAC unitconfigured to operate according to the IEEE 802.11a Standard and/or theIEEE 802.11n Standard). For example, the modified MAC unit is configuredto determine when the AP can transmit uplink signals with respect to areserved time period for uplink OFDMA, according to an embodiment.

FIG. 13 is a diagram illustrating the transmission of an uplink OFDMAdata unit 500 by a plurality of client stations, and the transmission ofACKs 504 by the AP in response to the uplink OFDMA data unit 500,according to an embodiment. In the scenario illustrated in FIG. 13, fourclient stations simultaneously transmit respective OFDM sub-channelblocks 508 to the AP. The OFDM sub-channel blocks 508 form the uplinkOFDMA data unit 500.

In the scenario illustrated in FIG. 13, the AP successfully receivedeach of the OFDM sub-channel blocks 508. In response, the AP transmitsan OFDMA data unit that comprises ACKs 504 corresponding to differentOFDM sub-channel blocks. In an embodiment, the OFDMA data unit thatcomprises the ACKs 504 has a format the same as or similar to a downlinkOFDMA data unit as described with respect to FIG. 5, the same as orsimilar to a downlink OFDMA data unit as described with respect to FIG.6, or has another suitable format.

The uplink OFDMA data unit 500 and the ACKs 504 are transmitted in atime period reserved for uplink OFDMA. A MAC unit of the AP has signaledeach of the client stations providing each client station with anindication of the time at which the client station can transmit thecorresponding OFDM sub-channel block 508. For example, according to anembodiment, the MAC unit of the AP provides uplink OFDMA time slotinformation to the client stations.

The ACKs are spaced from the OFDMA data unit 500 by a SIFS intervals. Inan embodiment, a MAC unit of a client station is configured to wait,after the corresponding OFDM sub-channel block, longer than the SIFSinterval for an ACK/NAK from the AP. In an embodiment, the MAC unit ofthe client station is configured to wait for a time out period forretransmission if an ACK/NAK from the AP is not received, wherein thetime out period is longer than the SIFS interval.

In an embodiment, the AP transmits Block ACKs after receiving severaluplink OFDMA data units.

According to an embodiment, the AP transmits a synchronization signal tothe client stations to help the client stations synchronize fortransmitting an uplink OFDMA signal. In an embodiment, thesynchronization signal is transmitted to the client stations as adownlink OFDMA signal. FIG. 14 is a diagram illustrating thetransmission of the uplink OFDMA data unit 500 being preceded by the APtransmitting downlink synchronization signals 520, according to anembodiment. In an embodiment, the synchronization signals 520 aretransmitted to the client stations as a downlink OFDMA signal. Thesynchronization signals 520 have the same duration, according to anembodiment.

In the embodiment according to FIG. 14, each client station transmitsthe corresponding OFDM sub-channel block 508 at a determined timeduration after receiving the corresponding synchronization signal 520.

FIG. 15 is a diagram illustrating communications in a WLAN 550 duringthree time periods: a first CSMA period 554, an OFDMA time period 558,and a second CSMA period 562. In FIG. 15, time progresses from left toright so that the first CSMA period 554 occurs first, the OFDMA timeperiod 558 occurs second, and the second CSMA period 562 occurs third.The WLAN includes an AP, a plurality of legacy client stations (LCs),and a plurality of OFDMA client stations (OC).

In the first CSMA period 554, the AP transmits a legacy downlink singleto one of the LCs. The OFDMA period 558 is reserved for uplink OFDMAsignal transmissions. Thus, in the OFDMA period 558, a plurality of OCstransmit an uplink OFDMA signal to the AP. The uplink OFDMA signalincludes a plurality of OFDM sub-channel blocks corresponding to theplurality of OCs. In the OFDMA period 558, the AP also transmitsACKs/NAKs (not shown) in response to the uplink OFDMA signal, accordingto an embodiment. According to an embodiment, in the OFDMA period 558,the AP also transmits synchronization signals (not shown) prior to theuplink OFDMA signal. In the second CSMA period 562, an LC transmits alegacy uplink transmission to the AP.

According to some embodiments, the above discussed OFDMA techniques areutilized in combination with simultaneous downlink transmission (SDT)techniques and simultaneous uplink transmission (SUT) techniquesdescribed in U.S. patent application Ser. No. 12/175,526, entitled“Access Point with Simultaneous Downlink Transmission of IndependentData for Multiple Client Stations,” filed on Jul. 18, 2008, and U.S.patent application Ser. No. 12/175,501, entitled “Wireless Network withSimultaneous Uplink Transmission of Independent Data from MultipleClient Stations,” filed on Jul. 18, 2008. Both of U.S. patentapplication Ser. No. 12/175,526 and U.S. patent application Ser. No.12/175,501 are hereby expressly incorporated by reference herein intheir entireties.

FIG. 16 is a flow diagram of an example method 600 that is implementedby an AP in a WLAN, according to an embodiment. At block 604, aplurality of different OFDM sub-channel blocks are assigned to aplurality of different client stations. At block 308, OFDM data unitsare received, wherein each OFDM data unit comprises a plurality ofdifferent OFDM sub-channel blocks transmitted by the plurality of clientstations simultaneously. In an embodiment, a plurality of independentdata streams are modulated in respective OFDM sub-channel blocks.

At block 612, the plurality of independent data streams are demodulated.

In another embodiment, the method includes transmitting asynchronization signal from the AP prior to receiving each OFDM signalat block 608.

FIG. 17 is a flow diagram of an example method 650 that is implementedby an AP in a WLAN, according to an embodiment. In an embodiment, themethod 650 is implemented in conjunction with the method 600 of FIG. 16.

At block 654, the AP determines a time period that is reserved foruplink OFDMA signals. At block 658, the AP transmits to the clientstations data indicative of the time period determined at block 654.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method, comprising: assigning, at a firstcommunication device, a plurality of different orthogonal frequencydivision multiplexing (OFDM) sub-channel blocks to a plurality of othercommunication devices including a second communication device and athird communication device, wherein the plurality of OFDM sub-channelblocks includes a first OFDM sub-channel block assigned to the secondcommunication device and a second OFDM sub-channel block assigned to thethird communication device, and wherein the second communication deviceand the third communication device are members of a wireless local areanetwork (WLAN); receiving, at the first communication device, data forthe second communication device; receiving, at the first communicationdevice, data for the third communication device; and generating, at thefirst communication device, an orthogonal frequency division multipleaccess (OFDMA) data unit, including generating a plurality of OFDM dataunits corresponding to the plurality of OFDM sub-channel blocks, whereineach OFDM data unit includes a respective preamble that occupies abandwidth equal to or less than a bandwidth of the corresponding OFDMsub-channel block, and wherein the data received for the secondcommunication device is modulated on sub-channels in the first OFDMsub-channel block and the data received for the third communicationdevice is modulated on sub-channels in the second OFDM sub-channelblock; wherein the data for the second communication device isindependent of the data for the third communication device; and whereinat least one of the OFDM sub-channel blocks is formatted tosubstantially conform to a physical layer specification of a WLANcommunication protocol having a maximum channel bandwidth smaller than abandwidth of the generated OFDMA data unit.
 2. A method according toclaim 1, wherein at least one of the OFDM sub-channel blocks isformatted to substantially conform to at least one of the physical layerspecification of the Institute for Electrical and Electronics Engineers(IEEE) 802.11a Standard and the physical layer specification of the IEEE802.11n Standard.
 3. A method according to claim 1, wherein at least oneof the OFDM sub-channel blocks is formatted to conform to a definedcommunication protocol specification so that the OFDM sub-channel blockincludes an OFDM data unit that conforms to the defined communicationprotocol specification.
 4. A method according to claim 1, whereingenerating the plurality of OFDM data units comprises including, in eachof the plurality of OFDM data units, a signal that indicates the OFDMdata unit is within an OFDMA data unit having one or more other OFDMdata units corresponding to one or more other communication devicesdifferent than the second communication and the third communicationdevice.
 5. A method according to claim 1, wherein generating theplurality of OFDM data units includes generating a first OFDM data unithaving a duration less than a duration of the OFDMA data unit.
 6. Amethod according to claim 5, wherein generating the plurality of OFDMdata units comprises: including in the first OFDM data unit anindication of the duration of the OFDMA data unit.
 7. A method accordingto claim 1, wherein generating the plurality of OFDM data units includesgenerating a first OFDM data unit corresponding to the secondcommunication device and a second OFDM data unit corresponding to thethird communication device; wherein the method further comprises zeropadding data for the second communication device so that a duration ofthe first OFDM data unit corresponds to a duration of the OFDMA dataunit.
 8. A method according to claim 1, wherein generating the OFDM dataunits comprises generating a first OFDM data unit corresponding to thesecond communication device and a second OFDM unit corresponding to thethird communication device; wherein a data rate of the first OFDM dataunit is different than a data rate of the second OFDM data unit.
 9. Amethod according to claim 1, further comprising transmitting the OFDMAdata unit.
 10. A method according to claim 9, further comprisingreceiving an OFDMA data unit including a plurality of acknowledgement ornegative acknowledgment signals transmitted simultaneously by the secondcommunication device and the third communication device.
 11. Anapparatus, comprising: a wireless local area network (WLAN) networkinterface device having one or more integrated circuit (IC) devices; anda physical layer (PHY) processing unit implemented on the one or more ICdevices, the PHY processing unit configured to: assign a plurality ofdifferent orthogonal frequency division multiplexing (OFDM) sub-channelblocks to a plurality of other communication devices including a firstcommunication device and a second communication device, wherein theplurality of different OFDM sub-channel blocks includes a first OFDMsub-channel block assigned to the first communication device and asecond OFDM sub-channel block assigned to the second communicationdevice, and form, using data received for the first communication deviceand data received for the second communication device, an orthogonalfrequency division multiple access (OFDMA) data unit that includes afirst OFDM data unit corresponding to the first OFDM sub-channel blockand a second OFDM data unit corresponding to the second OFDM sub-channelblock, wherein each of the first OFDM data unit and the second OFDM dataunit includes a respective preamble that occupies a bandwidth equal toor less than a bandwidth of the corresponding OFDM sub-channel block,and wherein the data received for the first communication device ismodulated on sub-channels in the first OFDM sub-channel block and thedata received for the second communication device is modulated onsub-channels in the second OFDM sub-channel block; wherein the data forthe first communication device is independent of the data for the secondcommunication device; and wherein each of the first OFDM data unit andthe second OFDM data unit is formatted to substantially conform to aphysical layer specification of a WLAN communication protocol having amaximum channel bandwidth smaller than a bandwidth of the generatedOFDMA data unit.
 12. An apparatus according to claim 11, wherein the PHYprocessing unit is configured to include, in each of a plurality of OFDMsub-channel block data units, a signal that indicates the OFDMsub-channel block data unit is within an OFDMA data unit having one ormore other OFDM data units corresponding to one or more othercommunication devices.
 13. An apparatus according to claim 11, whereinthe PHY processing unit is configured to generate the OFDMA data unit sothat one or both of (i) the first OFDM data unit and (ii) the secondOFDM data unit has a respective duration less than a duration of theOFDMA data unit.
 14. An apparatus according to claim 13, wherein the PHYprocessing unit is configured to include in the first OFDM data unit anindication of the duration of the OFDMA data unit.
 15. An apparatusaccording to claim 11, wherein the PHY processing unit is configured to:zero pad data for the first device so that a duration of the first OFDMdata unit corresponds a duration of the OFDMA data unit.
 16. Anapparatus according to claim 11, wherein a data rate of the first OFDMdata unit is different than a data rate of the second OFDM data unit.17. A method, comprising: assigning, at a first communication device, aplurality of different orthogonal frequency division multiplexing (OFDM)sub-channel blocks to a plurality of other communication devicesincluding a second communication device and a third communicationdevice, wherein the plurality of OFDM sub-channel blocks includes afirst OFDM sub-channel block assigned to the second communication deviceand a second OFDM sub-channel block assigned to the third communicationdevice, and wherein the second communication device and the thirdcommunication device are members of a wireless local area network(WLAN); receiving data for the second communication device; receivingdata for the third communication device; and generating an orthogonalfrequency division multiple access (OFDMA) data unit that includes afirst OFDM data unit and second OFDM data unit respectivelycorresponding to the first OFDM sub-channel block and the second OFDMsub-channel block, wherein the data received for the secondcommunication device is included in the first OFDM data unitcorresponding to the first OFDM sub-channel block, and wherein the datareceived for the third communication device is included in the secondOFDM data unit corresponding to the second OFDM sub-channel block;wherein each of the first OFDM data unit and the second OFDM data unitincludes a respective indication of a duration of the OFDMA data unit,and wherein at least one of (i) the first OFDM data unit and (ii) thesecond OFDM data unit has a respective duration different than theduration of the OFDMA data unit; and wherein at least one of the OFDMsub-channel blocks is formatted to substantially conform to a physicallayer specification of a WLAN communication protocol having a maximumchannel bandwidth smaller than a bandwidth of the generated OFDMA dataunit.
 18. A method according to claim 17, wherein data for the secondcommunication device is independent of the data for the thirdcommunication device.
 19. A method according to claim 17, wherein a datarate of the first OFDM data unit is different than a data rate of thesecond OFDM data unit.
 20. A method according to claim 17, furthercomprising transmitting the OFDMA data unit.
 21. A method according toclaim 20, further comprising receiving an OFDMA data unit including aplurality of acknowledgement or negative acknowledgment signalstransmitted simultaneously by the second communication device and thethird communication device.
 22. An apparatus, comprising: a wirelesslocal area network (WLAN) network interface device having one or moreintegrated circuit (IC) devices; and a physical layer (PHY) processingunit implemented on the one or more IC devices, the PHY processing unitconfigured to: assign a plurality of different orthogonal frequencydivision multiplexing (OFDM) sub-channel blocks to a plurality of othercommunication devices including a first communication device and asecond communication device, wherein the plurality of OFDM sub-channelblocks includes a first OFDM sub-channel block assigned to the firstcommunication device and a second OFDM sub-channel block assigned to thesecond communication device, and wherein the first communication deviceand the second communication device are members of a wireless local areanetwork (WLAN), receive data for the first communication device, receivedata for the second communication device, and generate an orthogonalfrequency division multiple access (OFDMA) data unit that includes afirst OFDM data unit and second OFDM data unit respectivelycorresponding to the first OFDM sub-channel block and the second OFDMsub-channel block, wherein the data received for the first communicationdevice is included in the first OFDM data unit corresponding to thefirst OFDM sub-channel block, and wherein the data received for thesecond communication device is included in the second OFDM data unitcorresponding to the second OFDM sub-channel block; wherein each of thefirst OFDM data unit and the second OFDM data unit includes a respectiveindication of a duration of the OFDMA data unit, and wherein at leastone of (i) the first OFDM data unit and (ii) the second OFDM data unithas a respective duration different than the duration of the OFDMA dataunit; and wherein at least one of the OFDM sub-channel blocks isformatted to substantially conform to a physical layer specification ofa WLAN communication protocol having a maximum channel bandwidth smallerthan a bandwidth of the generated OFDM data units.
 23. An apparatusaccording to claim 22, wherein data for the first communication deviceis independent of the data for the second communication device.
 24. Anapparatus according to claim 22, wherein a data rate of the first OFDMdata unit is different than a data rate of the second OFDM data unit.25. An apparatus according to claim 22, further comprising transmittingthe OFDMA data unit.
 26. An apparatus according to claim 25, furthercomprising receiving an OFDMA data unit including a plurality ofacknowledgement or negative acknowledgment signals transmittedsimultaneously by the first communication device and the secondcommunication device.
 27. An apparatus according to claim 25, whereinthe PHY processing unit comprises one or more transceivers.
 28. Anapparatus according to claim 27, further comprising: one or moreantennas coupled to the one or more transceivers.
 29. An apparatusaccording to claim 11, wherein the PHY processing unit comprises one ormore transceivers.
 30. An apparatus according to claim 29, furthercomprising: one or more antennas coupled to the one or moretransceivers.